German Published Patent Application No. 10 2009 004 487 describes a method for detecting the drowsiness of a driver, in which a measure for the severity of the inattentiveness and/or drowsiness of the driver is calculated from sensory data, the measure for the severity of the inattentiveness and/or drowsiness being ascertained based on data from a steering wheel angle sensor as a function of a steering rest phase and a subsequent steering action, a steering error being determined, and each steering error being linked to an assigned weighting factor.
German Published Patent Application No. 10 2005 057 267 and U.S. Patent Application Publication No. 2010/0039249, each of which is expressly incorporated herein in its entirety by reference thereto, describe a method for detecting the state of a driver, a signal signaling the state of the driver being generated as a function of the steering angle, the time characteristic of the steering angle being determined, and a signal representing the driver state as inattentive being generated at least in response to the presence of a typical time characteristic of the steering angle.
PCT International Published Patent Application No. WO 2008/052827 describes a method and a device for detecting the state of a driver, in which a signal characterizing the driver state is derived from the rate of occurrence of the minima in the time characteristic of a quantity which represents the lane-keeping behavior of the driver, in particular, the time which is necessary until the crossing of the lane marking.
German Published Patent Application No. 10 2005 031 311 describes a drowsiness warning system for drivers, having a detection device for the instantaneous detection of the driver drowsiness, having an evaluator, connected to the detection device, for determining an instantaneous drowsiness value, and having a warning device for warning the driver in the event the drowsiness value exceeds a threshold value determined in the evaluator, a device being provided for adapting the threshold in consideration of a drowsiness model of the driver, and the drowsiness model taking sleep information about the driver into account.